1. Field of the Invention
This invention relates to an optical disc, such as a DVD, which stores digitized audio and visual content, such as movies and music, and an optical disc which reads the recorded information on the optical disc.
2. Description of the Related Art
Outline of DVD Standard
One known type of optical disc for storing digital images is Digital Versatile Disc (DVD), which has been widely used mainly in storing and delivering of movie content all over the world. DVD is the standard determined by the DVD forum, which is open to the public as the DVD standard (DVD Book) (refer to www.dvdforum.org). The DVD standard has also been determined in International standards and JIS. Here, ECMA-267 is a document related to the International standard on 120 mm DVD-ROM, one of the DVD physical standards. Hereinafter, a brief explanation will be given referring to ECMA-267.
There are four types of 120 mm DVD-ROM: single-sided single layer, single-sided dual layer, double-sided single layer, and double-sided dual layer. In delivery of an accumulation of content, such as movies, there are two types of single-sided discs: one is a single-sided single layer disc with a capacity of 4.7 GB and the other is a single-sided dual layer disc with a capacity of 4.27 GB per layer (a total capacity of 8.54 GB per disc).
The development of a disc whose capacity is larger than that of the aforementioned DVD (referred to as the existing DVD) has been desired. This comes from a desire to store high-definition (HD) images into a single disc (temporarily referred to as the next-generation DVD).
[Non-Patent Document] ECMA-267
With the development of the next generation DVD, it will be possible to design a next-generation DVD device (drive or player) for the next-generation DVD so as to read not only the next-generation DVD but also the existing DVD. Since the next-generation DVD differs from the existing DVD in recording density, modulation system, signal processing, track format, and the like, a conventional DVD device (drive or player) cannot read the data from the next-generation DVD. That is, the conventional DVD device has the disadvantage of being unable to read not only HD movie content recorded on the next-generation DVD disc but also conventional DVD movie content recorded on the next-generation DVD, which may lead to a factor that hinders the spread of the next-generation DVD.